Monodisperse colloidal silica spheres

Monodisperse colloidal silica spheres with various surface coatings are of considerable interest to many fields, such as ceramics, colloids, catalysis, chromatography, and glass preparation. We are interested in these particles for their... 

Dense silica nanoparticles have received considerable attention since monodisperse colloidal silica spheres, obtained liom aimnoniacal TEOS solution, were reported in the late 1960s by Stober et aL [1]. These dense particles, more often being monodispersed with controlled particle size, a well-defined morphology, and a surface with silanol groups by which they could be functionalized, are used for a variety of commercial applications including colmants, fillers and pigments. 

A. van Blaaderen, J. van Geest, and A. Vrij Monodisperse colloidal silica spheres from tetraalkoxysilanes Particle formation and growth mechanism, J. CoUoid Interface Sci., 154 (1992)481-501... 

Tani T., Madler L., Pratsinis S.E., Synthesis of zinc oxide/silica composite nanoparticles by flame spray pyrolysis. J. Mater. Sci. 2002 37(21) 4627 632 Van Blaaderen A., Vrij A. Synthesis and characterization of colloidal dispersion of fluorescent, monodisperse silica spheres. Langmuir 1992a 8(12) 2921-2931 Van Blaaderen A.V., Van Geest J., Vrij A. Monodisperse colloidal silica spheres from tetraaUcoxysi-lanes Particle formation and growth mechanism. J. Colloid Interface Sci. 1992b 154(2) 481-501... 

Yamada, Y. Nakamura, T. Ishi, M. Yano, K., Reversible control of light reflection of a colloidal crystal film fabricated from monodisperse mesoporous silica spheres, Langmuir. 2006, 22, 2444 2446... 

The method relies on the properties of monodispersed latex/silica spheres to assemble, through colloidal interactions, into a well-ordered, face-centered-cubic colloidal crystal upon centrifugation, sedimentation, electrophoresis, oscillatory shear or pressing in the form of pellets. Following pre-assembly of the colloidal crystal template, the precursor is infiltrated into the empty octahedral and tetrahedral interstitial sites that exist between the spheres. After conversion of the precursor to the desired material inside the voids, the template is removed leaving... 

Monodispersed 35 nm colloidal silica spheres were used to template a periodic mesoporous polymer [71]. Divinylbenzene was used to make a cross-linked rigid polymer replica, ethylene glycol dimethacrylate ensured that it was flexible and shrinkable, while mixtures of the two were used to vary the degree of shrinkage. In addition, the mesoporous polymer replicas were themselves... 

In this section, experimental results obtained with several different experimental techniques and measured on several different colloidal silica dispersions are described and discussed. The ultimate goal of the investigations is the ability to synthesize stable, monodisperse colloidal model spheres from organoalkoxysilanes with different chemical compositions and surface properties (47-52). 

Stober, W., Fink, A., and Bohn, E.J. (1968) Controlled growth of monodisperse silica spheres in the micron size range. Colloid Interface Sci. 26, 62-69. 

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

It is difficult to obtain meaningful results on colloidal interactions unless the samples have low polydispersity. Studies of colloidal interactions between whole casein micelles can be affected by the polydispersity of native casein micelles. (Stothart,1987b). To circumvent the problem of polydispersity, the food system can be deposited on monodisperse silica spheres (Rouw and de Kruif,1989). 

A variety of methods have been demonstrated for crystallizing monodispersed spherical colloids (such as polymer beads and silica spheres) into long-range ordered lattices. Some of the commonly used ones include sedimentation, self-assembly via repulsive electrostatic interaction, ordering via attractive capillary forces, and crystallization under physical confinement. 

Another important method for photonic crystal fabrication employs colloidal particle self-assembly. A colloidal system consists of two separate phases a dispersed phase and a continuous phase (dispersion medium). The dispersed phase particles are small solid nanoparticles with a typical size of 1-1000 nanometers. Colloidal crystals are three-dimensional periodic lattices assembled from monodispersed spherical colloids. The opals are a natural example of colloidal photonic crystals that diffract light in the visible and near-infrared (IR) spectral regions due to periodic modulation of the refractive index between the ordered monodispersed silica spheres and the surrounding matrix. 

After an aqueous dispersion of monodispersed spherical colloids was injected into the cell, a positive pressure was applied through the glass tube to force the solvent (water) to flow through the channels. The beads were accumulated at the bottom of the cell, and crystallized into a three-dimensional opaline lattice under continuous sonication. So far, we have successfully applied this approach to assemble monodispersed colloids (both polystyrene beads and silica spheres) into ccp lattices over areas of several square centimeters. This method is relatively fast opaline lattices of a few square centimeters in area could be routinely obtained within several days. This method is also remarkable for its flexibility it could be directly employed to crystallize spherical colloids of various materials with diameters between 200 nm and 10 pm into three-dimensional opaline lattices. In addition, this procedure could be easily modified to crystalhze spherical colloids with diameters as small as 50 nm. ... 

Ordered porous carbons were synthesized by replication of colloidal templates made from 30 - 100 nm diameter silica spheres and removal of the silica templates using aqueous HP. To create the templates, the monodisperse particles were pressed into pellets and then sintered slightly at their points of contact. The silica template were filled with carbon precursor solution of divinylbenzene (DVB) and a free radical initiator, azobisisobutyronitrile (AIBN). Polymerization and carbonization of the precursor solution and subsequent dissolution of the silica templates leave a polycrystalline network of carbon with interconnected uniform pores. The degree of order of the silica template is faithfully reproduced in the carbon replicas. 

Crystalline colloidal arrays (CCA) are mesoscopically periodic fluid materials which efficiently diffract light meeting the Bragg condtion (/-. These materials consist of arrays of colloidal particles which self assemble in solution into BCC or FCC crystalline arrays (7,5) (Figure 1) with lattice constants in the mesoscale size range (50 to 500 nm). Just as atomic crystals diffract x-rays that meet the Bragg condition, CCA diffract UV, visible, and near IR light (2-4) the diffraction phenomena resemble that of opals, which are close-packed arrays of monodisperse silica spheres (6). 

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